Abstract [en]

Pd fullerene composites were first synthesized and studied in the early 90s by for example Nagashima et al. In this study we present a novel and rapid approach to synthesize Pd fullerides based on direct reaction of C60 with Pd2dba3. We show that the Pd fullerene polymer phase forms at temperatures around the melting point of Pd2dba3 (150 degrees C) and that it proceeds upon further annealing while releasing dba. The synthesis reactions were studied in TGA/DSC. TEM revealed that the material easily collapses under the electron beam into nanoparticles. Under very low doses almost no particles can be found. Similarly, Raman spectroscopy confirmed the formation of Pd fulleride polymers but also supported the collapse of the Pd fulleride phase when irradiated by high laser power. CVD experiments have been conducted on directly coated Si substrates showing similar results to previous reports, namely that Pd2C60 is an efficient catalysts for the growth of helical carbon nanofibers. Our study gives both insights into the formation of nanoparticles as well as the synthesis of C60 polymers. The method is also compatible with direct coating processes making it useful for a broad spectrum of CVD and catalysis applications. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Nitze, Florian

Umeå University, Faculty of Science and Technology, Department of Physics.

2013 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Carbon nanostructures are a wide field with many applications. The use of carbon nanostructures as support in heterogeneous catalysis is a key development that led together with the use of nanoparticles to a significant cost reduction of catalysts. Catalysts designed in this way are widely applied in fuel cell technologies. For portable devices especially low temperature fuel cells are desirable with low hazards for the user. One technology which fulfills these requirements is the direct formic acid fuel cell (DFAFC). DFAFC have many promising characteristics, such as high electromotive force and easy fuel handling. However, they still suffer from too low power output and lifetime for commercialization.

This thesis focusses on two main aspects: the synthesis of carbon nanostructures by chemical vapor deposition (CVD) and their application as catalyst support. The materials are investigated by many different techniques ranging from transmission electron microscopy (TEM) to fuel cell tests.

Different carbon nanostructures could be synthesized by catalytic CVD on palladium (Pd) nanoparticles. Multi-walled carbon nanotubes (MWCNTs), carbon nanofibers (CNFs) and helical carbon nanofibers (HCNFs) were grown, selectively, dependent on temperature, using acetylene as carbon precursor. Especially HCNF raised further interest due to their unique structure. A growth model for HCNFs was developed based on an anisotropic extrusion model. The synthesis conditions for HCNFs were optimized until an almost 100 % purity with very high efficiency was obtained.

The unique helical but fiber-like structure made the material very interesting as support for heterogeneous catalysis. Several catalysts based on Pd nanoparticle decorated HCNFs were developed. The synthesis methods ranged from standard methods like the polyol method to phase-transfer methods. The catalysts showed very promising results for the electro-oxidation of methanol, ethanol and formic acid. This makes them highly attractive for fuel cell applications. The catalysts were tested in DFAFC. The superiority of HCNF-based catalysts is attributed to the good attachment of nanoparticles to the defect-rich and easy to functionalize surface of HCNFs in combination with adequate film forming properties during electrode preparation.